Epigenetic alterations contribute to all stages of tumor progression and it is well recognized that aberrant DNA methylation and histone hypoacetylation of growth control genes and tumor suppressor genes directly contribute to malignancy. Because epigenetic changes are reversible, these alterations represent attractive targets for promising new anticancer agents and this property has been exploited recently for new therapies. While recent progress has lead to the FDA approval of the first two epigenetic therapies the mechanistic basis for their efficacy is poorly understood. This proposal will explore entirely new links between a relatively unexplored class of deacetylases (the sirtuins) and proteins that bind to methylated DNA (methyl-CpG binding proteins) in gene silencing. These advances could help explain why some solid tumors are refractory to the current epigenetic therapies and provide a more complete mechanism by which tumor suppressor genes (TSGs) become heritably silenced. Elucidating the molecular basis for this epigenetic silencing of growth control genes and TSGs is important for identifying novel anticancer therapies and we propose to do the following: Specific Aim 1 - Determine the role of methyl-CpG binding proteins in targeting SIRT1 to endogenous hypermethylated gene promoters. Specific Aim 2 - Determine the contribution of methyl-CpG binding proteins and SIRT1 in regulating chromatin structure at silenced growth control and tumor suppressor genes. Specific Aim 3 - Determine the functional significance of MeCP2 acetylation and deacetylation by SIRT1.